docs: def midi_event(self, event_type, channel, param1, param2=None):
          """Convert and return the paraters as a MIDI event in bytes."""
          assert event_type < 0x80 and event_type >= 0
          assert channel < 16 and channel >= 0
          tc = a2b_hex('%x%x' % (event_type, channel))
          if param2 is None:
              params = a2b_hex('%02x' % param1)
          else:
              params = a2b_hex('%02x%02x' % (param1, param2))
          return self.delta_time + tc + params